Butterfly valve assemblies have found frequent use in recent years in fluid distribution systems, such as water, chemical and sewage systems, wherein the mains or pipes are of relative large diameters. These valves usually employ a large circular vane or disc usually rotatable or pivotable on a displaced axis in a fluid passage extending through a valve body member. The disc is movable from a closed position where it engages a seat carried in the valve body member to provide a seal against leakage in the fluid main, to an opened position where it is effectively in a somewhat streamlined alignment with the axis of the flow of fluid in passage through the valve body member so as to permit free substantially non-turbulent flow therethrough the valve assembly. In the design of these butterfly valve assemblies, it is a highly desirable design criteria to provide a seat which will be effective for the life of the valve assembly as it is often difficult and expensive to remove and replace the seat in the field. Additionally, it is an important design criteria to provide a seat in a butterfly valve which permits the valve assembly to be installed in a fluid main or pipe regardless of the direction of flow of fluid therethrough.
Heretofore, efforts have been made to design butterfly valve assemblies with a seat construction which would obviate the difficulties encountered from wear but such prior efforts have not been entirely satisfactory because of the expense involved in manufacture and further, because the seats would not accommodate for wearing conditions during the life of the valve and especially would not accommodate for use of the valve with flow in either direction.
In the prior art of seat construction for butterfly valve assemblies, systems have been employed wherein a recess was provided in the passage of the valve body member and a rubber or rubber-like resilient material was molded into the recess for cooperating with the valve disc. This type of construction failed to completely eliminate leakage resulting from tolerance accumulations and slight manufacturing errors and it was unusually difficult to replace the seat in the field without special equipment. Replaceable and adjustable rubber or rubber-like seats were used, but again such seats did not fully reach the desired design criteria.
Accordingly, hard, corrosive resistant metal seats were used and these seats were either machined directly into the valve body member which required the body member to be made from an expensive corrosive resistant material or were machined on inserts supported in the valve body. In some instances these metal seats were mechanically attached by cementing or threading the seat to the valve body member, or by circumferentially cold forging a seat ring onto a body receiving surface or by positioning a seat ring in a recess in one section of a body member and retaining it there by another section of a body member. In each instance the seat when assembled in the body member of the valve assembly had no axial movement in the passageway and thus after prolonged operating periods where there could be wear to the seat itself or wear to the resilient sealing ring on the valve disc, leakage could result because of no accommodation for this wear. This resulted in either replacing the resilient ring on the valve disc or replacing and/or refinishing the seat. Furthermore, such valve assemblies, wherein the seat in the body member had no axial flexibility for small limits of axial movement, were not particularly adapted to accommodate for flow through the valve assembly in either direction.